Oxygen tends to move from a gas containing a high concentration of oxygen to one of lower concentration. If the two gases are separated from each other by an oxygen ion conductor, oxygen will dissociate on one surface of the conductor and absorb electrons to form oxygen ions. These oxygen ions can then diffuse through the ionic conductor, leaving the entry surface with a deficiency of electrons. Emerging on the exit or low oxygen concentration side of the ion conductor, oxygen ions give up electrons to form molecular oxygen, leaving the exit surface with an excess of electrons. Thus, an electrical potential difference, or EMF, is set up between the two surfaces of the ion conductor. The greater the difference in oxygen content of the two gases, the greater will be the tendency of oxygen to diffuse through the conductor, and the greater will be the potential difference between the entry and exit surfaces.
These basic principles underlie the operation of oxygen sensing devices, which are generally well known in the art. Oxygen sensors function by monitoring the EMF developed across an oxygen ion conductor which is exposed to gases having different oxygen partial pressures. The reciprocal principle underlies the operation of oxygen separators (also called oxygen generators) such as disclosed in U.S. Pat. No. 4,296,608. Voltage is applied to an oxygen ion conducting material and oxygen ions will be forced to flow across the material such that one gas will become richer in oxygen than the other, resulting in a basic oxygen generator. A physical structure for an oxygen generator composed of an oxygen ion conducting material is disclosed in U.S. Pat. No. 5,205,990 and is highlighted in prior art FIGS. 1-3 in the present application and the entire disclosure is hereby incorporated by reference.
In prior art FIG. 1, an oxygen generator 10 includes a ceramic honeycomb body 12 made of an oxygen ion conducting material, for example, bismuth oxide, having a first plurality of channels 14 and a second plurality of channels 16 extending therethrough from a front face 18 to a back face 20. The channels 14 and 16 are arranged in alternating rows, resembling a striped pattern laterally across faces 18 and 20 of the ceramic honeycomb body 12. The oxygen generator 10 further includes a voltage source 22 electrically connected to the channels 14 and 16 through electrode connectors 24 and 26 which are located on a top portion 28 of the ceramic honeycomb body 12, respectively. The connection methodology is such that each of the first channels 14 are electrically connected in parallel and each of the second channels 16 are also electrically connected in parallel. The voltage source 22 is operable to apply a voltage across the electrodes 24 and 26 such that a voltage potential is created across the first and second channels 14 and 16, thereby enabling oxygen ion conduction through the ceramic honeycomb body 12 from one channel to another.
The oxygen generator 10 receives a source gas 30 containing some oxygen, for example, air, into the first channels 14 which are open on both the front face 18 and back face 20 of the body 12. The oxygen ions pass through the oxygen ion conducting material of the body 12 from the first channels 14 to the second channels 16 which are sealed on both the front face 18 and back face 20 of the body 12. In this manner the source gas 30 contains more oxygen than an exit gas 32 from the back face 20 due to the conduction of oxygen ions into the second channels 16. The oxygen 34 within the second channels 16 is collected from a side face 36 of the body 12 via a plurality of third channels 38 which laterally intersect the second channels 16 approximately in the middle of the side face 36.
Prior art FIG. 2 is another oxygen generator 40 which employs the same basic structure as the oxygen generator 10 in prior art FIG. 1. FIG. 2, however, due to a fewer number of channels, is helpful in illustrating how the first and second channels 14 and 16 extend through the body 12 from the front face 18 to the back face 20. FIG. 2 also further illustrates the manner in which the second channels 16 are sealed at the front and back faces 18 and 20. The second channels 16 are sealed with plugs 42 on both the front face 18 and the back face 20 to prevent dilution or contamination of the generated oxygen in the second channels 16. FIG. 2 also illustrates the voltage potential that exists across the channels 14 and 16 via the "+" and "-" signs 43 resident on several of the channels via the voltage source 22 and the electrode connectors 24 and 26. Lastly, FIG. 2 illustrates in greater detail the third channels 38 that traverse the second channels 16 laterally and intersect the side face 36 at holes (or apertures) 44 which form a straight line pattern vertically along the side face 36 of the body 12.
The manner in which generated oxygen is removed from the second channels 16 in the prior art oxygen generators 10 and 40 of FIGS. 1 and 2 is illustrated in greater detail in prior art FIG. 3. Note that in FIG. 3 the orientation of the oxygen generator has been rotated 90 degrees such that the front face 18 and the back face 20 are located on the bottom and top of the figure, respectively. Each of the plurality of second channels 16 is sealed at the front and back faces with a plug 50 which extends laterally across each of the channels 16. Plug 50 seals the channels 16 in a manner similar to the individual plugs 42 of FIG. 2 and is illustrated as a single plug for ease of illustration. Either a single plug 50 or multiple plugs 42 have been used with prior art devices. The generated oxygen is collected through the hole 44 on the side face 36. Each of the channels 16 are intersected with holes 52 which align with the hole 44 such that oxygen 34 is collected from each of the channels 16. The holes 44 and 52, which extend through the body 12 to intersect each of the channels 16, are formed by drilling a hole through the side face 36. This hole, however, is drilled without knowledge of registry and problems may arise as is illustrated in prior art FIG. 4.
Prior art FIG. 4 illustrates a limitation of the prior art oxygen generators 10 and 40 of FIGS. 1 and 2. FIG. 4 illustrates the result of either poor registry of the honeycomb body 12 or errant drilling of holes 44 and 52 through the second channels 16 of the device. If the registry of the body 12 is poor, that is, if the striped, alternating pattern of first and second channels 14 and 16 is not straight, the holes 52 caused by drilling may not intersect each of the second channels 16, thereby resulting in an inefficient collection of oxygen since oxygen would not be collected from a channel 54. Worse, the holes 52 may even intersect a first channel 14 (not shown) which would fundamentally impair the device by contaminating the collected oxygen 34 in the second channels 16 with the first gas 30 (e.g., air) in the first channels 14.
Likewise, if registry of the body 12 is adequate and the hole drilled through the body 12 to intersect the channels 16 is skewed, a similar undesirable result will occur. The problem of poor registry or skewed hole drilling is further compounded by the fact that one cannot easily detect either problem since the honeycomb body 12 is a substantially closed structure (meaning that holes are drilled without knowledge of registry), thereby preventing an easy visual detection of either failure mode.